<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 300px;
            height: 200px;
            border: 1px solid green;
            /* display: inline; */
        }
        #div5 {
           width: 100px;
           height: 50px;
           border: 1px solid red;
           margin: 10px;
           padding: 20px;
        }
        #div1 {
            margin: 10px;
            margin-bottom: 10px;
            padding: 10px;
        }

    </style>
</head>
<body>
    <div id="div1">
        <div id="div5">这是第一个div</div>
    </div>
    <div id="div2">这是第二个div</div>
    <div id="div3">这是第三个div</div>
    <div id="div4">这是第四个div</div>
</body>
</html>